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But the tests showed the investment banks with the largest exposure to capital markets came out among the weakest: Goldman's Tier 1 capital ratio fell to 6.3 per cent, JPMorgan 6.5 per cent, and Morgan Stanley 6.2 per cent.

The worst performer, as in last year's stress tests, was Zions Bancorp of Salt Lake City, which barely topped the minimum with a core capital ratio of 5.1 per cent.

Also coming in low in the severe-crisis scenario was BBVA Compass Bancshares, at 6.3 per cent.

But as a group the banks were stronger than in the 2014 tests, and it was the first time that no bank had fallen under the 5.0 per cent level since the tests began in 2009.

Their average actual Tier 1 capital ratio going into the test was 11.9 per cent, up from 11.5 per cent a year ago. In the test the group average fell to 8.2 per cent, compared with 7.6 per cent last year.

"The largest US-based bank holding companies continue to build their capital levels and to strengthen their ability to lend to households and businesses during a period marked by severe recession and financial market volatility," the Fed said.

The tests, instituted in the wake of the 2008 crisis which bared extreme vulnerabilities in the banking system, sought to determine if individual banks and the system as a whole could weather a prolonged recession in which the economy contracts 4.5 per cent in one year and the unemployment rate shoots up four percentage points.

That scenario wiped out US$490 billion worth of bank assets, close to the amount in last year's tests, but overall the banks proved they could stand the test.

The tests added this year the impact of a series of corporate defaults to which the investment banks would be most vulnerable.

Goldman barely topped another key measure of strength, the total risk-based capital ratio. At the end of the test it had 8.1 per cent, just above the minimum 8.0 per cent threshold.

The Fed made no comment on individual banks, but noted the steady improvement of the industry overall since the crisis.

"Our supervisory stress tests are designed to ensure that these banks have enough capital that they could continue to lend to American businesses and households even in a severe economic downturn."

The tests form the basis of the Federal Reserve's review of banks' capital plans, crucially whether they can distribute benefits to shareholders via dividends and share buybacks that effectively reduce their capital base.

Those judgements will come from the Fed next week.

Frank Keating, president of the American Bankers Association, said that with total industry capital of US$1.7 trillion, the tests show that banks "are well positioned to continue serving as a critical driver of our economic growth going forward."